No doubt the erstwhile resources minister - before the recent citizenship scandal broke - will try to press the energy giant to commit extending the plant's operations another five years to 2027.

But, as a dozen or more journalists visiting the site learned on Tuesday, there are a multitude of reasons why that doesn't make a lot of sense.

Or as Kate Coates, the general manager of the AGL Macquarie unit, puts it when describing the plant's partial failure during February's heatwave: "Liddell is an old lady: we can't ask [her] to run a marathon a few days in a row without her falling over."

It's likely Canavan will be told about the recent tube leak that roared like a jet engine - so loud, in fact, workers were dispatched to residents across Lake Liddell to explain why they couldn't hear themselves think.

Or the senator may visit the site of where, in March 2016, another leak caused so much pressure to build up that a 10kg door was sent flying 100 metres.

The din inside the 46-year-old plant, with its grimy coal mills pulverising the fuel and its labyrinth of steam-filled pipes, is bad enough. But on our visit, two of the four 420-megawatt units [already down from the original 500MW rating] were out for maintenance - and may well be still offline when Canavan parades through.

One of the two units is out of action for a few weeks for scheduled maintenance. The other, unit 2, has apparently developed a "wobble" when the turbine cranks up towards 3000 revolutions per minute, and AGL is "struggling to find the issue", Coates says.

That unit, as it happens, was one of the two to fail when the state needed electricity most during that February heatwave when NSW set statewide heat records two days in a row.

The most dramatic recent failure, though, came in 2015 when unit 1 had a "run down without oil". Instead of slowing down in about 40 minutes, the turbine ground down in about a quarter of that time. It took nine months to be put back in service.

No wonder that a "desktop" study conducted in 2013 looking into the cost of extending the life of Liddell out to 2032 estimated it would cost $900 million - a figure likely to be higher at today's costs. AGL will spend close to $300 million keeping it functioning until 2022.

As Tim Nelson, AGL's chief economist, notes, the energy market is also moving on. Coal-fired power stations can provide the "dispatchable" power needed to meet demand, but they can't do it very flexibly - taking up to a day to crank up.

As Nelson pointed out, vintage plants like Liddell are few in the world, with just 1 per cent older than 50 years.

In Liddell's case, the company worries with reason about its reliability even within that timeframe. Its coal use has been rationed since October because of difficulties of getting the fossil fuel, a problem that dogs its [much younger] sister plant, Bayswater and other Hunter Valley power plants.

"We will just keep scrabbling for contracts," Coates says, adding that its also a battle to get coal "over a very, very busy rail network".

For someone who began working as an apprentice electrical fitter in 1981 and rose through the ranks as an engineer at several power plants, Coates is no great fan of coal.

She notes the efficiency of Liddell, with all its extant and emerging faults, is roughly 35 per cent, with the rest of energy lost through heat and driving its own plant including giant fans. [And 910 kilograms of carbon dioxide is emitted per megawatt-hour too.]

Even the high efficiency, lower emissions plants often hailed by Canavan and other coal booster, only run about 5-7 percentage points better. "We lose a great deal of that energy," she says.

Super-critical power plants have made technological progresss, operating with steam heated to 700 degrees celsius versus about 500 at Liddell, Coates before adding: "Having said that, I still don't think we should be building coal-fired power stations."